1. Field of the Invention
Embodiments of the present invention generally relate to a downhole tool for hydrocarbon production and method for using same. More particularly, embodiments of the present invention relate to a propellant assembly for subsurface fracturing and method for using same.
2. Description of the Related Art
To recover hydrocarbons from subterranean formations, a wellbore is drilled to some depth below the surface. The wellbore can then be lined with tubulars or casing to strengthen the walls of the borehole. To further strengthen the walls of the borehole, the annular area formed between the casing and the borehole can be filled with cement to permanently set the casing in the wellbore. The casing can then be perforated using a perforation tool that is lowered into the wellbore from the surface. The perforated casing allows the hydrocarbon fluids to enter the wellbore and flow to the surface of the well.
There is an increasing interest in producing hydrocarbon fluids from potentially productive geological formations that contain a sufficient volume of such fluids, but have low permeability so that production is slow or difficult. Low permeability can be naturally occurring due to the geological conditions of the formation. Low permeability can also be caused by damage to the formation from drilling, cementing, and perforating operations. Further, mature wells can incur similar damages in the form of migration of fine particulates, pipe scaling, wax buildup, and other conditions that reduce formation permeability and restrict flow.
One was to increase production and permeability within the formation is a technique known as artificial stimulation. One method of artificial stimulation is “well fracturing.” Generally, a sufficient hydraulic pressure is applied against the formation to break or separate the earthen material to initiate a fracture in the formation. A fracture is an opening that extends laterally from the well and improves permeability within the formation so hydrocarbon fluids can flow.
The hydraulic pressure can be generated by pumping a fracturing fluid from the surface through the wellbore into the formation. Alternatively, hydraulic pressure can be generated by combusting propellants within the wellbore to expel high pressure gas. In this fashion, a work string having a perforating gun attached thereto is lowered into the well casing cemented into the wellbore. The perforating gun is positioned adjacent to the formation to be fractured. The perforating guns are then fired to produce an explosion of high pressure gas that is sufficient to penetrate the casing, surrounding cement, and formation.
Perforating guns known in the art utilize shaped propellant charges, such as those disclosed in U.S. Pat. Nos. 4,391,337; 6,006,833; and 6,851,471. US Publication 2003/0155112 discloses cylindrical propellant charge. However, there are numerous challenges to igniting such charges and producing long and even burn rates. Once ignited, short and fluctuating burn rates can limit fracture propagation and can increase the likelihood of damage to the wellbore.
Furthermore, fractures have a tendency to close or collapse once the pressure in the formation is relieved. To prevent such closing when the fracturing pressure is relieved, the fracturing fluid can include a granular or particulate material, referred to as a “proppant.” The proppant is left behind in the fracture even after the fluid pressure is relieved. Ideally, the proppant holds the separated earthen walls of the formation apart to keep the fracture open and provides flow paths through which hydrocarbons from the formation can flow.
A variety of proppants have been used depending on the geological conditions of the formation. Proppants include particulate materials, such as sand, glass beads, and ceramic pellets, which create a porous structure. As such, the hydrocarbon fluid is able to flow through the interstices between the particulate material.
However, the pressure of the surrounding rock in the formation can crush the proppants over time. The resulting fines from this disintegration tend to migrate and plug the interstitial flow passages in the proppant. These migratory fines drastically reduce the permeability, lowering the conductivity of the hydrocarbon fluid. Conductivity is a measure of the ease with which the hydrocarbon fluid can flow through the proppant structure and is important to the productivity of a well. When the conductivity drops below a certain level, the fracturing process is repeated or the well is abandoned.
There is a need, therefore, for a new well tool and method for perforating and stimulating subterranean wells. There is also a need for a perforating tool that utilizes a proppant having a higher crush resistance.